People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

The Science Behind Adrenaline and Why It Won't Give You Super Strength

Can adrenaline turn a 97-pound weakling into the Hulk? Nah. But it's a still pretty damn cool hormone. Eneas De Troya, CC BY 2.0

It’s an experience no doubt familiar to everyone who has experienced a moment of fear, stress, or excitement: a rapidly beating heart, keener senses, and an almost limitless supply of energy. For a few minutes at least.

That momentary burst of oomph is largely started by our body’s ramped up production of the hormone adrenaline (and its accompanying partner chemical, noradrenaline).

Since its discovery at the turn of the 20th century, adrenaline has come to be associated with all sorts of phenomenal feats and attributes: from resurrecting the dead to either turning people into temporary superheroes or reckless addicts enticed by the very prospect of danger (adrenaline junkies). As with most things, though, the real truth lies somewhere in the still very cool middle. So let’s go ahead and take a honest look at the little hormone with a big impact.

Flight-or-Fight

Adrenaline, at its simplest, is part of our innate response mechanism to perceived external stress. When something threatening or exciting comes into our rear view mirror, the body undergoes a series of subtle internal changes to better prepare for and/or avoid whatever’s headed our way. These adjustments are collectively called our "flight-or-fight" response.

For those particularly inclined to step in front of danger, though, such as skydivers, there’s probably room to include a third “F” — Fling.

When flight-or-fight kicks in, adrenaline is primarily released from its namesake organ smushed on top of our kidneys, the adrenal gland. Working in synergy with noradrenaline (mostly released from our central nervous system), adrenaline is pumped throughout the body via the bloodstream and, depending on which cells it comes into contact with, prompts a multitude of effects.

A short, though not exhaustive, tally of adrenaline’s influence includes increased heart rate and glucose production, better respiration, and more efficient oxygen use by our muscles, which in turn boosts our strength, speed and endurance. Because it temporarily helps shut down our immune response and other non-essential bodily functions, adrenaline is even used to treat severe allergic attacks, or anaphylaxis.

If our body was a tricked out, fleshy street racer, adrenaline could best be thought of as our nitro fuel, ready to jump in at a moment’s notice and push us over the finish line.

Cart Before The Horse

Crucial as adrenaline is to our survival, its close relationship to how we experience excitement and fear has led early scientists and the public alike to overstate its powers, according to Dr. Brian Hoffman, professor of medicine at Harvard Medical School. Hoffman would know better than most, being the author of the 2013 book Adrenaline, a self-styled biography of the hormone.

For instance, when we talk about seeking an “adrenaline rush,” we’re likely thinking about it in terms of a recreational drug — as if the very release of adrenaline will turn us into insta-daredevils, similarly to something like cocaine. But that’s mostly wrong.

“The adrenaline flowing [into our bodies] is a consequence of excitement,” explained Hoffman. ”It doesn’t cross the brain-blood-barrier, so it probably doesn’t directly affect our sense of excitement.” In other words, we’re not excited or scared because adrenaline courses through our body, adrenaline courses through our body because we’re excited or scared.

There’s a chance that adrenaline can have subtle effects on our mental state, similar to how forcing someone to smile can trigger a sense of happiness, but as Hoffman noted, we haven’t been able to find conclusive evidence of that in the lab.

Likewise, adrenaline, while certainly a performance enhancer, isn’t a miracle-maker. “It’s very important in Olympic athletes, where a tiny, tenth of a percent, [boost] can be the difference between winning a Gold medal and losing...But in terms of the ordinary physiology of humans, the effects of adrenaline secretion are more modest,” Hoffman said. “There’s no evidence that a shot of adrenaline could turn a 97-pound weakling into someone who could lift a car, obviously.”

How about those stories of desperate mothers doing such a thing to save their kids? Well, that’s likely due to the ubiquity of urban legends and exaggerated tales of heroism (lifting a car off someone may seem inhuman, but lifting one a few inches off the ground for a few seconds probably isn’t).

And people certainly can be and are addicted to the very idea of danger — it’s just not adrenaline they’re really after.

Amazing Adrenaline

None of this is to take away from the awesomeness of adrenaline, mind you. As Hoffman sharply explains in his book, it was the first hormone to be discovered. From that discovery, and further exploration of how adrenaline worked, emerged an entire field of biology (endocrinology), numerous scientific breakthroughs in unlocking how other important chemicals and drugs interact with the human body, and a large cabinet’s worth of Nobel Prizes.

For those morbidly wondering, you can indeed die from adrenaline. Hoffman briefly details the case of a Massachusetts nurse who was sentenced to life for having artificially caused cardiac arrests in several of her patients through adrenaline injections, and it’s likely the so-called “ broken heart syndrome,” caused by extreme bursts of emotion and which can be fatal, is partly triggered by too much adrenaline. It might also be partly to blame for the slight uptake of heart problems following a natural disaster or the growth of a tumor that pumps out excess adrenaline.

In the end, though, adrenaline remains one of the most essential hormones in our body. It’s also a lifesaving drug in our medical toolbox, since it can jumpstart a sluggish heart and help with resuscitation — just don’t expect it to bring back the dead all by its lonesome.